Kitchen Chemistry Experiment 23
Glurch

What is a colloid? How do you make a colloid? What are the differences between fluids and non-newtonian fluids?

 

Materials	Substitutions
white glue
liquid laundry starch
sodium chloride	table salt
large beaker	jar or zip lock bag
graduated cylinder	measuring cup &tablespoon
ruler
newspaper

Procedure

1. Place 30 ml (2 tablespoons) white glue in a large beaker.
2. Add 3.5 grams (1/2 teaspoon) sodium chloride to 60 ml (1.4 cup) liquid laundry starch.
3. Pour sodium chloride/laundry starch mixture into the white glue. Mix well.
4. Over the sink, pour the mixture into your hand and squeeze out the excess liquid.
5. Kneed the colloid until smooth.
6. Roll the colloid into a small ball. Lift the ball about 30 cm above the counter surfure and drop. Measure the height the ball bounces.
7. Flatten the ball into a disk. Stretch the colloid until it just breaks. Measure the combined length of the two pieces. Are they the same length?
8. Press the colloid onto a piece of newspaper. Check to see if any ink was absorbed by the colloid.

 

Extensions

1. Does the colloid bounce?
2. How would you describe the glurch's elasticity or stretchability?
3. Will the sample absorb ink?
4. Assume you just invented this colloid and was trying to sell it. How would you attempt to market the colloid?
5. Repeat the experiment using various amounts of sodium chloride. How does this affect the physical properties of the colloid?

Teacher's Notes

Colloids are a type of mixture which will not settle out. The particles are too large to dissolve but small enoung to remain suspended in the solvent.

Increases in temperature will change the molecular motion of the solvent allowing more of the colloid to be suspended. Therefore, increases in temperature will cause the colloid to become more sticky and pliable.

Glurch will bounce. Student answers will vary. Glurch has less "stretchability" than SILLY PUTTY--see this lab manual. Have your students compare and contrast the colloids in this lab manual (Slime, Silly Putty, and Glurch) with store bought "slimes".